This invention relates generally to gas turbine engines and more particularly to methods and systems to enhance transition duct cooling within gas turbine engines.
At least some known gas turbine engines ignite a fuel-air mixture in a combustor to generate a combustion gas stream that is channeled to a turbine via a hot gas flow path. Compressed air is channeled to the combustor from a compressor. Known combustor assemblies generally use fuel nozzles that channel fuel and air to a combustion region of the combustor. The turbine converts the thermal energy of the combustion gas stream to mechanical energy that rotates a turbine shaft. The output of the turbine may be used to power a machine, for example, an electric generator or a pump.
At least some known combustor assemblies include a transition duct or transition piece that channels combustion gases from the combustor assembly towards the turbine assemblies. At least some known transition ducts include perforated cooling sleeves that surround the transition piece to channel cooling air for cooling of the transition piece. However, known cooling sleeves may cause uneven cooling of the transition pieces which may increase temperature gradients that may reduce the operational life of the combustor hardware. As a result, portions of the combustor may require replacement more frequently than if the transition piece was more uniformly cooled. To compensate for higher temperatures and/or thermal gradients, some known combustors include components fabricated from materials that are more resistant to thermal stresses and/or wear. However, such components increase the costs and/or weight to the engine, as compared to engines having combustors that do not include such components.
Other known combustor assemblies include a cooling system for the transition duct that includes a hollow cooling sleeve. Known cooling sleeves include a plurality of channels and elaborate cooling passages formed therein that channel cooling flow around the transition piece to facilitate cooling thereof. However, such cooling sleeves are generally difficult to fabricate and increase the manufacturing costs of the combustor assembly. Moreover, the complex cooling circuits included within such sleeves may reduce cooling performance if any of the cooling passages become obstructed and/or plugged by contaminants. Reduced cooling effectiveness may cause increased operating temperatures, increased thermal gradients, and/or increased thermal stresses in the transition piece. To accommodate higher temperatures and/or thermal gradients, at least some known combustors include components that are fabricated from materials that are more resistant to thermal fatigue. However, other such components may be more expensive to manufacture as compared to components that are fabricated without such materials.